Geography of San Bernardino County, California

Source: Wikipedia. Pages: 53. Chapters: Calico Early Man Site, California Historical Landmarks in San Bernardino County, California, Chino Valley, California, Colorado Desert, Colorado River Aqueduct, Colorado River Indian Reservation, Cucamonga Valley AVA, Fort Mojave Indian Reservation, Geology of the Death Valley area, High Desert (California), Joshua Tree National Park, Lake Mojave, Low Desert, Maria fold and thrust belt, Mojave Desert, Mojave National Preserve, Mojave Road, Mountain Pass rare earth mine, Naval Air Weapons Station China Lake, Places of interest in the Death Valley area, R-2508 Special Use Airspace Complex, Rainbow Basin, San Andreas Fault, San Bernardino meridian, San Gorgonio Wilderness, San Jacinto Fault Zone, South Coast AVA, Starvation Flats, Whipple Mountains Wilderness. Excerpt: The exposed geology of the Death Valley area presents a diverse and complex set of at least 23 formations of sedimentary units, two major gaps in the geologic record called unconformities, and at least one distinct set of related formations geologists call a group. The oldest rocks in the area that now includes Death Valley National Park are extensively metamorphosed by intense heat and pressure and are at least 1700 million years old. These rocks were intruded by a mass of granite 1400 Ma (million years ago) and later uplifted and exposed to nearly 500 million years of erosion. Marine deposition occurred 1200 to 800 Ma, creating thick sequences of conglomerate, mudstone, and carbonate rock topped by stromatolites, and possibly glacial deposits from the hypothesized Snowball Earth event. Rifting thinned huge roughly linear parts of the supercontinent Rodinia enough to allow sea water to invade and divide its landmass into component continents separated by narrow straits. A passive margin developed on the edges of these new seas in the Death Valley region. Carbonate banks formed on this part of the two margins only to be subsided as the continental crust thinned until it broke, giving birth to a new ocean basin. An accretion wedge of clastic sediment then started to accumulate at the base of the submerged precipice, entombing the region's first known fossils of complex life. These sandy mudflats gave way about 550 Ma to a carbonate platform which lasted for the next 300 million years of Paleozoic time. The passive margin switched to active margin in the early-to-mid Mesozoic when the Farallon Plate under the Pacific Ocean started to dive below the North American Plate, creating a subduction zone; volcanoes and uplifting mountains were created as a result. Erosion over many millions of years created a relatively featureless plain. Stretching of the crust under western North America started around 16 Ma and is thought to be caused by upwelling from the subducted spread